Hilborn EFI System Testing - Seriously Stacked

Are individual runner induction systems all they’re cracked up to be? We test a Hilborn EFI system against dual carbs to find out.

As an unsophisticated gender that's easy to please, males dig things that are stacked. It doesn't matter if it's a cheeseburger, potato chips in a can, or something far less politically correct. There are much better magazines for studying up on that last one, so we won't even go there. For boys and their toys, the same goes for induction systems. No one gawks enviously at a dual-plane intake manifold, or goes gaga over the plastic monstrosity that is a modern EFI intake. Instead, it's the tunnel-rams and sheetmetal manifolds that captivate our imagination, and perhaps the King of visual induction system punch is an individual-runner, eight-stack intake. They certainly have an undeniable raciness to them. Style alone is reason enough for some people to bolt these intakes onto their motors, but do they actually improve horsepower and torque output over a carb, or are they merely eye-candy that lacks any real substance? To find out, we swapped a dual-carb intake manifold for a Hilborn EFI system on a 482 ci W-engine, then hit the dyno.

Although 1964 is often considered the unofficial beginning of the muscle car era, Chevy was cranking out plenty of sweet rides before then. The '61 and '62 Bel Air and Impala are among the best looking Chevys ever built, but by today's standards, the W-series big-blocks that powered them aren't quite up to snuff. To modernize the W in his '61 Bel Air, Jeff Cameron of Dooley and Sons Rods and Customs gave it a complete modern makeover. The 409 was stroked to 482 ci using a 454 crank, and then topped with out-of-the-box, unported Edelbrock aluminum cylinder heads, a dual-quad intake manifold, and a pair of 500cfm carbs. With a Comp 254/254-at-0.050 hydraulic roller cam actuating the valves, Jeff was pleased with the overall performance of the motor, but sought to tame it down a bit for around-town cruising.

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"I wanted to improve the drivability and fuel mileage of the motor by upgrading to EFI, but there aren't a lot of options out there for these motors. I thought a Hilborn eight-stack induction system would look great on the Gen I big-block, so I was eager to test it out," Jeff explains.

Hot rodders these days are smart enough to know that the horsepower potential of an engine is most heavily influenced by cylinder head airflow. What many people neglect to realize is that the best heads in the world will never reach their full potential if they're choked up by a junk intake manifold. The problem is that intake manifold design, by nature, is a compromise from the get-go. If you design an intake manifold for maximum airflow, it's going to take up a lot of space. This universal truth is why NHRA Pro Stockers—or just about any race car for that matter—have such massive hoodscoops. Air doesn't like to change directions, which is why it's incredibly difficult to convince speeding air molecules to negotiate a 90-degree turn from the intake plenum into the runners, followed by another 90-degree turn from the runners into the intake ports. Tunnel-ram intakes address these issues by positioning the plenum as high above the motor as possible, thereby straightening the induction path between the plenum and cylinder heads. The long intake runners of a tunnel-ram greatly enhance air speed as well, boosting airflow through the intake ports and into the cylinders.

Unfortunately, big scoops you can hardly see over aren't an option for street cars. The ugly truth is that the most important yet most uninteresting factor that goes into intake manifold design is often underhood clearance. Even if it was possible to tastefully fit a tunnel-ram intake in a street car, the design still has its flaws. Whether the intake manifold in question is a dual-plane, single-plane, tunnel-ram or a factory EFI design, all conventional intakes feature runners that share a common plenum. This isn't an issue with conservative factory-spec camshafts, but with long-duration performance cams that hold the intake valve open well past BDC, the result is a reversion pulse that shoots back through the intake port and runners, and into the plenum.

"In a high-rpm race motor, intake reversion isn't an issue, but it's very detrimental at lower rpm in a street car. When you have reversion pulses from eight different cylinders coming into a single shared plenum, it pushes the air around into different directions, which reduces flow," explains Andrew Starr of Hilborn Injection. "Since an individual-runner intake manifold doesn't have a common plenum, it prevents the reversion pulse from one cylinder from adversely affecting the airflow in another cylinder. The benefit is extremely smooth part-throttle drivability, which is a function of not having a reversion pulse in the intake tract to deal with."

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Hilborn EFI System Testing - Seriously Stacked

1. Removing the existing induction system is as straightforward as it gets. After draining the cooling system, the air cleaner, coolant hose, fuel line, and throttle cable were removed before unbolting the intake manifold and pulling it off.

3. In a conventional dual- or single-plane intake manifold, vacuum accessories often pick up their vacuum signal by tapping into the plenum. Since an individual-runner intake manifold doesn’t have a common plenum, vacuum is picked up off of the bottom of each runner. Brass fittings from the runners hook up to a centrally mounted distribution block using -6AN hoses. From the block, vacuum can be distributed to accessories such as the distributor or brakes.

4. According to Hilborn, a round intake runner produces more air speed that any other shape. As such, the round bores of the intake runners measure 2 7/16-inch at the butterflies, and then transition into a rectangular shape in order to mate up with the intake ports on the cylinder heads. To maximize charge density, the injectors are positioned up high in the runners.

5. The steel ram tubes are cadmium plated for durability. Since Jeff had no intentions of cutting a hole in the Bel Air’s hood, the ram tubes were cut down by five inches using a bandsaw. This left 1/2-inch of clearances between the air horn and the bottom of the hood.

6. Electronic fuel injection offers many benefits, but the miles of wiring it requires isn’t one of them. Jeff hid the injector harness inside a piece of custom bent 1/2-inch stainless steel tubing. The tubing screws into each side of the manifold, and the injector connector hooks up to the main harness at the back of the motor.

7. Gen I blocks have dimples on the lifter valley rails that help position the intake oil seal gaskets. Installing the Hilborn lifter valley plate requires drilling and tapping these holes to a 1/4-20 thread. Afterwards, the valley plate can be secured to the block with allen bolts.

8. After bolting the driver side injector manifold to the head, it was time to address the coolant lines. Unlike a traditional intake manifold, the Hilborn design does not have provisions for internal coolant passages. Jeff’s solution was fabbing up a custom distribution log from 5/8 inch stainless tubing that’s fed by two 1/2-inch hard lines attached to the rear coolant outlets on each cylinder head. From there, another 1/2-inch tube directs coolant from the log up to the thermostat housing. A second line sends coolant from the log to the heater core.

9. With the passenger side injector manifold bolted down, the injector harness was connected to the fuel injectors. At 42 lb/hr of flow, the injectors are good for more than 600 hp.

10. Another area in which the Hilborn manifold deviates from the factory design is that it does not have a mounting pad for the thermostat housing. Instead, the Hilborn kit includes a remote-mount Moroso housing. Jeff made a custom stainless bracket to mount the thermostat housing to the water pump. Two short sections of -8AN hose, along with four 90-degree hose ends, connect the front cylinder head water passages to the housing.

11. The throttle cable attaches to an actuation arm located on the very back of the driver side injector manifold. When the throttle is actuated, motion is transferred to the passenger side throttle shaft with a centrally mounted linkage. It features a tension rod and several set screws for easy adjustment.

12. The ram tubes slide inside each intake runner, and are then cinched down with the integrated pinch clamps. The bell on the ram tube doesn’t look like much, but cutting it off will reduce horsepower output substantially.

13. For a super clean installation, the FAST computer was mounted beneath the dash. This location made it easy to route the wiring harness through a one-inch hole that was drilled in the firewall, directly above the trans tunnel area. The harness includes connections for the injector harness, MAP sensor, distributor, throttle-position sensor, and coolant temperature sensor. Most of them were routed in the lifter valley area to keep them out of sight.

15. The X-frame chassis of the ’61-’64 Bel Air can make it a challenge to route exhaust systems, but they provide an excellent mounting point for fuel lines. Jeff ran a 1/2-inch stainless hard line from the fuel tank to the firewall area, at which point it hooks up to a flexible -8AN hose. The hose then connects to the driver side fuel rail.

16. The fuel pressure regulator was mounted directly to the frame, adjacent to the starter. This makes it nearly invisible from under the hood, but still allows easy access for pressure adjustments. With the new feed line attached, the old feed line now functions as the return line after hooking it up to the return port on the regulator.

17. Once back under the hood, Jeff put the finishing touches on the fuel system. A -8AN feed line sends fuel to the driver side rail, and fuel is then directed to the passenger side rail using a -6AN crossover hose. From there, fuel exits from the rear of the passenger side fuel rail and connects to the pressure regulator with a -6AN hose.

18. With its oh-so-pretty scalloped valve covers, a W-series big-block is already one slick looking lump. Not only does an eight-stack induction add to the visual sizzle, but it packs substantial performance improvements as well. After firing the motor up, Jeff set the idle speed at 900 rpm by adjusting the idle stop screws on each injector manifold.

19. The Hilborn EFI system can be had with either a Carabine ECU that’s programmable with a hand-held tuner, or a FAST XFI computer. Jeff opted for the enhanced flexibility and precision of the FAST system.

20. On the School of Automotive Machinists’ Dynojet, the big-block performed best with the air/fuel ratio dialed in at 13.0:1. The Hilborn setup improved upon the baseline pull of 236 rear-wheel horsepower by tacking on another 20 numbers.

21. Peak numbers aren’t everything. Although the Hilborn EFI system picks up just 1 lb-ft of torque at peak, it absolutely destroys the carbs in the low- and mid-range. From 3,600-4,200, the difference in the area under the curve is phenomenal.

22. With the dual carbs, the big-block falls flat at 4,300 rpm, and is out of breath by 4,900. The Hilborn EFI setup, on the other hand, doesn’t experience this dip in power, and keeps on pulling to 5,200 rpm.

23. Dyno numbers are one thing, but how does the new Hilborn setup feel on the street? Jeff reports: “The drivability improvement is through the roof compared to the carbs. There’s a night and day difference, especially at low rpm. The throttle response is so much better, and the car is now much more fun to drive.” The ’61 has a 700-R4 trans and 10-bolt rear, making it an ideal street machine.

Since the small-block in our 1971 Chevy Corvette project car was already built when we got the car, an engine dyno wasn't an option, so we decided to test different induction systems in a fun way: at the dragstrip. - Vette Magazine » Read More